Lyme disease is the most prevalent vector-borne disease affecting human health in the U.S. This project is designed to develop a basic understanding of the population ecology of the deer tick lxodes dammini and factors that regulate the population in southern New York State where Lyme disease has become epidemic. We intend to provide sound ecological basis for improved efforts to understand and control populations of the tick vector of Lyme disease. We will use novel approaches to determine the absolute density of l. dammini populations at field study sites. These estimates will form a basis for calibrating the accuracy of tick sampling methods. The accuracy of host animal examinations, carbon-dioxide-baited tick traps, and drag cloth sampling methods will be determined in field study sites with varying tick densities. We will explore natural population regulation in l. dammini by comparing an established population that has stabilized its growth rate with one that has only recently become established and is still increasing. We will construct a life table for each l. dammini population and determine the rates of mortality for all active stages. The major factors regulating the abundance of l. dammini at each site will be examined by distinguishing off-host mortality from on-host mortality. Mortality due to environmental factors such as temperature and humidity, as well as predators, parasites, and pathogens will be investigated as sources of off-host mortality. Tick feeding and molting success will be used to investigate on-host mortality and will contribute toward understanding the role of host immunity in regulating l. dammini populations in nature. Thus, we will identify important sources of natural mortality that can be exploited to artificially reduce the density of l. dammini populations and the risk of Lyme disease to humans.